Secretion and absorption (methods and functions).

With the development and wide availability of endoscopic procedures, the importance of secretion and absorption tests for the diagnosis of gastrointestinal diseases has decreased. Still, only in about half of the patients with abdominal complaints an organic cause can be established by imaging techniques and/or conventional laboratory tests. In the other patients diagnosis may partly be clarified by gastrointestinal function tests. This chapter focuses on indications, practical performance and interpretation of tests of gastrointestinal secretion and absorption (for breath tests compare chapter 5). Some tests of gastrointestinal secretion and absorption are so old that the original publications can no longer be located, particularly since the tests have been modified over the years. They are still included in this chapter if there is no more modern test available for measurement of a specific function. If not otherwise specified, the descriptions of how the tests are conducted stem from the author's own experience.